Polyester resin can have excellent mechanical strength, chemical resistance, electrical characteristics, precision moldability, and the like, as well as a good appearance, and thus is used for various applications. Further, polyester resin can be molded in combination with various forms of inorganic materials to increase mechanical strength, which can expand the ranges of applications for such resins.
However, since polyester resin generally has some degree of crystallinity, molded products made of the same can exhibit significant shrinkage as compared to a non-crystalline resin, and thus there is a need for improved dimensional stability. Dimensional stability of polyester resin can be improved while maintaining the benefits of polyester resin by partially mixing a non-crystalline resin such as a polycarbonate, acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylate (ASA), and the like with polyester resin. For example, ASA resin can be mixed with polyester resin for applications requiring weather resistance.
In addition, although mechanical strength of polyester resin increases in proportion to the content of fillers, specific gravity also increases as the filler content increases and mechanical strength does not increase once the amount of filler exceeds a certain point. This is an obstacle to the expansion of applications for polyester resin, and many studies have attempted to overcome this problem.
Since polyester resin may have good mechanical properties if it is reinforced with glass fiber, it is frequently used as a material for supporting high weight parts in automobiles. However, such material alone does not constitute a product but is assembled with other materials, and since polyester resin which is crystalline has a large shrinkage ratio compared to a non-crystalline resin, dimensional stability of a molded product may differ depending on injection conditions which can cause problems during assembling processes. Therefore, ASA resin that has excellent weather resistance and is non-crystalline and thus is capable of compensating for the drawback of polyester resin can be used as a resin mixed with the polyester resin.
However, the use of many conventional glass fibers can generate a stress difference in the resin according to the arrangement of the glass fiber, which can result in warpage of the resin.